The present invention relates generally to inflatable vehicle occupant restraint systems and more particularly to devices for controlling the inflation and deflation of air bag cushions for such systems.
In the design of inflatable occupant restraint systems for automotive vehicles, it is customary to provide a flexible bag that is arranged in fluid communication with a gas generating device or a source of gas under pressure to expand from some folded or stored position remote from a vehicle occupant to an expanded position in which the occupant's motion is cushioned. This inflating process necessarily happens rather rapidly in the functioning of such systems, occurring in a time on the order of 0.060 seconds. The cushioning effect of such systems is enhanced by the controlled deflation of the bag from its fully inflated position in a predictable manner. This deflation is generally accomplished through the provision of outlet ports formed through the bag which direct a portion of the pressurized inflating fluid to the atmosphere. It is known to provide "on-off" valve mechanisms at these outlet ports. U.S. Pat. No. 4,243,822 to Lipkin is exemplary of this broad approach. It is also known to provide apertures through the bag which are covered by a gas permeable cloth such as is disclosed in U.S. Pat. No. 4,097,065 to Okada et al. and U.S. Pat. No. 4,181,325 to Barnett. Even further, it is known to provide blow-out patches over air bag discharge ports which will rupture upon appropriate inflation. U.S. Pat. No. 3,580,603 to Chute et al. and U.S. Pat. No. 3,762,741 to Fleck et al. are exemplary of such approaches.
A common disadvantage of all of the prior art teachings in regard to the handling of discharge gas flow out of an air bag is that none provide a control of the flow responsive to changes in pressure within the bag and in flow out of the bag to provide for any variable control of discharge flow. In addition, the predictability and repeatability of the prior art fixed closures for discharge ports, such as the blow-out patches previously mentioned may be less than desirable for certain designs.